#!/usr/bin/env python3

def fb(num):
    if num <= 2:
        return 1
    return fb(num - 1) + fb(num - 2)

def main():
    num = int(input("请输入数字: "))

    n1 = 1
    n2 = 1
    r = 1

    for i in range(2, num):
        r = n1 + n2
        n2 = n1
        n1 = r

    print("fb = ", r, ", fb def = ", fb(num))

if __name__ == "__main__":
    main()
